In semiconductor manufacturing, plugs are used to connect conducting layers, such as metals and doped layers. FIGS. 1-3 show cross-sectional views of a semiconductor substrate 100, illustrating the steps of a conventional method for forming a plug. Turning to FIG. 1, an insulating layer 102 is deposited atop the substrate 100. Next, a contact opening 104 is formed by etching through the insulating layer 102. Then, a barrier metal layer 106 is deposited into the contact opening 104 and atop the insulating layer 102. A first conducting layer 108 is deposited into the contact opening 104 and atop the barrier metal layer 106.
Turning to FIG. 2, the portion of the first conducting layer 108 atop the insulating layer 102 and the portion of the barrier metal layer 106 atop the insulating layer 102 are removed by chemical mechanical polishing (CMP). The portion of the first conducting layer 108 inside the contact opening 104 remains to form a plug 110.
Turning to FIG. 3, a second conducting layer is deposited atop the plug 110 and the first insulating layer 102. Using conventional photolithography and etching techniques, portions of the second conducting layer are removed, leaving a conductive structure 112 above the plug 110. The etching is controlled to stop at the first insulating layer 102. As shown in FIG. 3, the plug 110 and the conductive structure 112 may not be in full contact. This undesirable result may occur because of misalignment between the conductive structure 112 and the plug 110 or because of differing dimensions between the conductive structure 112 and the plug 110.
What is needed is an improved method for forming a plug having an increased contact area.